GnuPG: www.gnupg.org [1]
RFC 2440: www.rfc-editor.org/rfc/rfc2440.txt [2]
Philip Zimmermann: www.philzimmermann.com [3]
Diceware Passphrase Home Page: www.diceware.com [4]
Wikipedia: Passphrase Article: www.wikipedia.org/wiki/Passphrase [5]
GnuPG HOWTOs: www.gnupg.org/documentation/howtos.html [6]
Links:
[1] http://www.gnupg.org
[2] http://www.rfc-editor.org/rfc/rfc2440.txt
[3] http://www.philzimmermann.com
[4] http://www.diceware.com
[5] http://www.wikipedia.org/wiki/Passphrase
[6] http://www.gnupg.org/documentation/howtos.html